1. Field of the Invention
This invention generally relates to integrated circuits, and more particularly to an integrated circuit package having an inductance loop formed from at least one input/output pin of the package. The invention also relates to a system which is at least partially controlled by the inductor loop of the package.
2. Description of the Related Art
One perennial goal among circuit designers is to decrease the size of integrated circuits. This goal is largely driven by market demand for ever-smaller consumer electronics, communications devices, and display systems to mention a few. There are, however, a number of impediments that undermine this goal, one of which will now be discussed.
Many integrated circuits are not self-contained devices. To ensure proper operation, these circuits must therefore be connected to one or more external components through connections which do not involve the use of an IC package input/output pin. This is accomplished, for example, by connecting the integrated circuit chip 1 to an off-package component 2 using bonding wires 3, as shown in FIG. 1. The need to establish off-package connections increases the cost and complexity of the manufacturing process and therefore is considered highly undesirable. These connections also expose the integrated circuit to an increased risk of damage from external influences, which translate into degradation in reliability and performance.
One conventional integrated circuit requiring off-package connections is routinely used in the frequency synthesizer of mobile communications devices such as cellular phones. Because the phase noise specifications are so stringent in these devices, voltage-controlled oscillators in a phase-locked loop used to generate the frequencies are typically based on some resonant structure. Ceramic resonators and LC tank circuits are common examples. While details in the implementation of LC tank oscillators differ, the general resonant structure includes an inductor connected in parallel with a fixed capacitor (C) and a variable capacitor (Cx). In the absence of any losses, energy passes between the capacitors and the inductor at a frequency fout=(½π) [L (C+Cx)]−1/2, with the inductance value L selected to control the operating band of the device.
In an integrated circuit which includes the aforementioned frequency synthesizer, the inductor used for band-selection purposes is located off-package (i.e., is circuit-board mounted). The use of off-package or board-mounted inductors increases system costs. Moreover, connection problems may occur between the package and board which may adversely affect the reliability and performance of the PLL circuitry.
Attempts have been made to overcome the drawbacks of these conventional devices. One approach, disclosed in U.S. Pat. No. 6,323,735, forms an inductor entirely within the integrated circuit package containing the phase-locked loop circuitry. This is accomplished using conductive wires which connect bonding pads on the IC chip to a same bonding pad on the package substrate. The connection between the pads and wires forms an inductance loop which controls the operational frequency band of the PLL circuitry. Multiple bonding pads may be included on the package substrate to form inductor loops of varying length. The loops are then selectively activated to effect a change in operational frequency.
The approach taken in the '735 patent is undesirable for at least two reasons. First, in order to form the inductor loop completely within the IC package, the package substrate must be formed to include bonding pads separate from the input/output package pins. The need to form these special pads increases the cost and complexity of the manufacturing process. Second, in order to accommodate the bonding pads, the size of the integrated circuit substrate must be increased and as a result more circuit board space is consumed. These effects undermine the goal of increasing integration and miniaturization.
Another approach, disclosed in the text “Wireless CMOS Frequency Synthesizer Design,” authored by Craninckx, discloses a self-contained integrated circuit package containing an inductor loop. This loop is formed by connecting bonding wires between bonding pads on the IC chip and respective input/output pins of the IC package. The input/output pins are then connected by a third bonding wire. While this approach does not require the formation of special bonding pads on the package substrate, it is has at least two drawbacks that make it undesirable. First, like in the '735 patent, a bonding wire is used to connect the input/output pins. As previously noted, these wires are susceptible to damage during manufacture and/or use. Second, the input/output pins connected by the third bonding wire are located on opposite sides of the package. As a result, the third wire must pass over the IC chip. This is undesirable because the wire could short certain portions of the chip circuitry and introduce noise and other interfering influences which substantially degrade chip performance.
In view of the foregoing considerations, it is apparent that a need exists for an integrated circuit package which is more economical and requires fewer processing steps to manufacture than conventional IC packages, and which is also less susceptible to damage and noise which can degrade reliability and performance not only of the chip circuitry but also the host system of the chip. A need also exists for an integrated circuit package which is self-contained at least with respect to connection of an inductor loop connected to the chip, and which is able through this connection to achieve at least one of the aforementioned advantages.